Rotating damper

ABSTRACT

A rotary damper (D) is constituted by: housings ( 11, 51 ); a silicon oil ( 21 ) being housed inside the housings ( 11, 51 ); a rotor ( 31 ) wherein a resistive portion ( 36 ) moving through the silicon oil  21  inside the housings ( 11, 51 ) is provided in an axial portion ( 32 ) which is housed inside the housings ( 11, 51 ) and projects from the housings ( 11, 51 ); and an O-ring ( 61 ) preventing the silicon oil ( 21 ) from leaking between the axial portion ( 32 ) and the housing ( 51 ), and multiple arc-like through-bores ( 37 ) are provided in the resistive portion ( 36 ) on a concentric circle, and depressed grooves ( 38 ) communicating with the arc-like through-bores ( 37 ) are provided. Accordingly, during the assembly, the air being mixed into the housing is not allowed to be excessively compressed, so that even if the rotor rotates bi-directionally, the noise being caused by the air being mixed into the housing can be prevented.

TECHNICAL FIELD

The present invention relates to a rotary damper for damping therotation of a driven gear which engages with, for example, a gear orrack.

BACKGROUND OF THE ART

A rotary damper disclosed in the Japanese Patent Publication No. 4-34015is constituted of: a housing; viscous fluid being housed inside thehousing; a rotor wherein a resistive portion moving through the viscousfluid inside the housing is provided in an axial portion which is housedinside the housing and whose one part projects from the housing; and asealing member which prevents the viscous fluid from leaking between theaxial portion of the rotor and the housing. A driven gear is attached tothe axial portion projecting from the housing.

In the above-mentioned conventional rotary damper, the resistive portionhas a roughly oval shape so that the air being mixed into the housingwhen the rotary damper is assembled is not allowed to be located betweenthe resistive portion of the rotor which is a part of torque occurrenceand the bottom face or ceiling face of the housing.

However, since the rotor rotates bi-directionally, when the air beingmixed into the housing climbs over the resistive portion and moves tothe opposite side of the resistive portion, the air makes a noise.

The noise which occurs when the air being mixed into the housing climbsover the resistive portion is regarded as a plosive sound being causedby the following. When the air being mixed into the housing climbs overthe resistive portion after the air being mixed into the housing iscompressed by climbing over the resistive portion, the air being mixedinto the housing is rapidly opened so that the plosive sound is made.

Incidentally, the higher the degree of viscosity the viscous fluid has,the easier the noise is made. Also, the narrower the distance betweenthe rotor and housing is, the easier the noise is made.

The purpose of the invention is to provide a rotary damper whichprevents the noise being caused by the air being mixed into the housing.

DISCLOSURE OF INVENTION

A rotary damper of the invention is constituted by: a housing; viscousfluid being housed inside the housing; a rotor wherein a resistiveportion moving through the viscous fluid inside the housing is providedin an axial portion being housed inside the housing and whose one partprojects from the housing; and a sealing member which prevents theviscous fluid from leaking between the axial portion and the housing. Inthe rotary damper, multiple air retention portions are provided in theresistive portion in a circumferential direction and an air movementpassage connecting the air retention portions is provided.

Also, in the rotary damper of the invention, the air retention portionsare formed by through-bores, and the air movement passage is formed by adepressed groove.

In addition, in the rotary damper of the invention, the multiple airretention portions are formed on a concentric circle, and the airmovement passage includes a circumferential groove corresponding to theair retention portions and being provided in the housing.

Also, in the rotary damper of the invention, the multiple air retentionportions are formed between the outer circumferential surface of theresistive portion and the inner circumferential surface of the housingin a circumferential direction.

According to the invention, as described in the above, the multiple airretention portions (through-bores) are provided in the resistive portionin a circumferential direction, and the air movement passage (depressedgroove) connecting the air retention portions (through-bores) isprovided, so that when the rotary damper is assembled, the air beingmixed into the housing can be moved from one air retention portion(through-bore) to another air retention portion (though-bore) in a statewherein the air being mixed into the housing is not excessivelycompressed.

Therefore, even if the rotor rotates bi-directionally, the noise beingcaused by the air being mixed into the housing can be prevented.

Moreover, the multiple air retention portions are formed on a concentriccircle, and the air movement passage includes the circumferential groovebeing provided in the housing and corresponding to the air retentionportions. Accordingly, when the rotary damper is assembled, the airbeing mixed into the housing can be moved from one air retention portionto the other air retention portion in a state of being additionallycompressed, so that the noise being caused by the air being mixed intothe housing can be additionally prevented.

Also, since the multiple air retention portions are formed between theouter circumferential surface of the resistive portion and the innercircumferential surface of the housing in a circumferential direction,when the rotary damper is assembled, the air being mixed into thehousing can be moved from one air retention portion to the other airretention portion without being additionally compressed, so that thenoise being caused by the air being mixed into the housing can beadditionally prevented.

Also, since the multiple air retention portions are formed between theouter circumferential surface of the resistive portion and the innercircumferential surface of the housing in a circumferential direction,when the rotary damper is assembled, the air being mixed into thehousing can be reliably located in the air retention portions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a first embodiment of a rotarydamper of the present invention;

FIG. 2 is a cross-sectional view of a rotor of the rotary damper in FIG.1;

FIG. 3 is a plan view of the rotor shown in FIG. 2;

FIG. 4 is a bottom plan view of the rotor shown in FIG. 2;

FIG. 5 is a cross-sectional view of the rotor constituting the rotarydamper of the second embodiment of the invention;

FIG. 6 is a plan view of the rotor shown in FIG. 5;

FIG. 7 is a bottom plan view of the rotor shown in FIG. 5;

FIG. 8 is an exploded perspective view of the third embodiment of therotary damper of the invention;

FIG. 9 is a cross-sectional view of the fourth embodiment of the rotarydamper of the invention;

FIG. 10 is a perspective view of the rotor of the rotary damper in FIG.9;

FIG. 11 is an exploded perspective view of the fifth embodiment of therotary damper of the invention;

FIG. 12 is an expanded sectional view of the left half of the rotarydamper shown in FIG. 11;

FIG. 13 is a plan view of the rotor of the rotary damper shown in FIG.11;

FIG. 14 is a front view of the rotor shown in FIG. 13;

FIG. 15 is a bottom plan view of the rotor shown in FIG. 13;

FIG. 16 is a cross-sectional view taken along line XVI-XVI in FIG. 13;

FIG. 17 is an expanded sectional view of the left half of a cap of therotary damper shown in FIG. 11;

FIG. 18 is an explanatory drawing of an assembling process of the rotarydamper in FIG. 11;

FIG. 19 is a fragmentary explanatory drawing of the assembling processof the rotary damper in FIG. 11; and

FIG. 20 is a cross-sectional view of the state wherein the rotary damperin FIG. 11 is assembled.

PREFERRED EMBODIMENTS FOR OPERATION OF INVENTION

The present invention will be explained with reference to the attachedfigures in detail.

FIG. 1 is a cross-sectional view showing the first embodiment of arotary damper of the present invention; FIG. 2 is a cross-sectional viewof a rotor of the rotary damper in FIG. 1; FIG. 3 is a plan view of therotor shown in FIG. 2; and FIG. 4 is a bottom plan view of the rotorshown in FIG. 2.

In FIG. 1, the reference alphabet D represents the rotary damperincluding: a plastic case 11; a silicon oil 21 as viscous fluid beinghoused inside the case 11; a plastic rotor 31 wherein a resistiveportion 36 moving through the silicon oil 21 inside the case 11 isprovided in an axial portion 32 which is housed inside the case 11 andwhose one part projects from the case 11 to the outside; and athrough-bore 52 wherein the axial portion 32 of the rotor 31 penetrates.The rotary damper D is constituted by: a plastic cap 51 blocking anopening of the case 11; an O-ring 61 as a sealing member preventing thesilicon oil 21 from leaking between the cap 51 and the axial portion 32of the rotor 31; and a plastic driven gear 71 being attached to theaxial portion 32 of the rotor 31 projecting from the cap 51.

Incidentally, the housing is constituted by the case 11 and the cap 51.

The above-mentioned case 11 is constituted by: a case main body 12wherein a cylindrical wall portion 14 circling the outer edge of abottom portion 13 whose planar shape is a circle is provided; acylindrical axial supporting portion 16 being provided at the center ofthe bottom face of the bottom portion 13; and mounting flanges 17 withmounting bores 18 being provided around the outer circumference of thecase main body 12, for example, in a radial direction at intervals of180 degrees.

On the bottom face of the bottom portion 13, a circumferential groove 13a corresponding to arc-like through-bores 37 described hereinafter isprovided on a concentric circle centering on the center of the axialsupporting portion 16 as an air movement passage.

Also, on the upper side of the cylindrical wall portion 14, a circlingthin-walled projecting cylinder portion 14 a whose inner circumferentialface is the extended face of the inner circumferential face of thecylindrical wall portion 14 is provided.

Incidentally, the reference numeral 15 represents a housed portion beingformed inside the case main body 12, and the housed portion is a partwherein the silicon oil 21 is housed and represents a lower part fromthe thin-walled projecting cylinder portion 14 a.

The rotor 31 is constituted by: a cylindrical axial portion 32; and atabular resistive portion 36 which is continuously provided in the axialportion 32 and circular in plan view.

A cylindrical cavity 33 wherein the axial supporting portion 16 of thecase 11 engages to be able to rotate is provided on the bottom surfaceof the axial portion 32. I-cut step portions 34 which are cut in anI-shape are provided in a part projecting from the cap 51, and fittinggrooves 35 are provided in flat surface parts (vertical surfaces) whichare cut in the I-shape in a horizontal direction, respectively.

Also, as shown in FIGS. 2-4, in the resistive portion 36, multiplearc-like through-bores 37 are provided on a concentric circle centeringon the center of the axial portion 32 as the air retention portion. Atthe same time, depressed grooves 38 communicating with the arc-likethrough-bores 37 are provided on a concentric circle of the arc-likethrough-bores 37 as the air movement passage.

Incidentally, the depressed grooves 38 are provided above and below(both sides) of the resistive portion 36.

The through-bore 52 wherein the axial portion 32 of the rotor 31penetrates is provided at the center of the cap 51. A diameter-expansionstep portion 53 which is cylindrically cut out in such a way of reachingto the lower end and houses the O-ring 61 is provided on the lower sideof the through-bore 52. Moreover, a circling fitting depressed groove 55wherein the thin-walled projecting cylinder portion 14 a of the casemain body 12 fits is provided on the outer edge of the lower side.

Also, an I-cut mounting bore 72 is provided at the center of the drivengear 71, and fitting projections 73 fitting into the fitting grooves 35being provided in the axial portion 32 of the rotor 31 are provided inthe flat surface parts of the mounting bore 72.

Next, an example of assembling of the rotary damper D will be explained.

First, after the axial portion 32 of the rotor 31 is fitted into theO-ring 61 and the silicon oil 21 is applied to the cavity 33 and theresistive portion 36, one part of the axial portion 32 and the resistiveportion 36 are housed inside the housed portion 15 in such a way thatthe axial supporting portion 16 of the case 11 is fitted into the cavity33.

After an appropriate amount of the silicon oil 21 is injected into thehoused portion 15, the thin-walled projecting cylinder portion 14 a isfitted into the fitting depressed groove 55 of the cap 51 while theaxial portion 32 is inserted into the through-bore 52, and an opening ofthe case 11 is blocked by the cap 51.

Herewith, when the opening of the case 11 is blocked by the cap 51, airE inside the thin-walled projecting cylinder portion 14 a is mostlydischarged out of the case 11, and the thin-walled projecting cylinderportion 14 a and the cap 51 are attached. At the same time, the O-ring61 is housed inside the diameter-expansion step portion 53, so that theO-ring 61 prevents the silicon oil 21 from leaking between the axialportion 32 and the cap 51.

Next, the thin-walled projecting cylinder portion 14 a and the cap 51are welded and sealed, for example, in such a way of circling with highfrequency welding.

When the axial portion 32 projecting from the cap 51 is pressed into themounting bore 72 of the driven gear 71, the fitting projections 73 arefitted into the fitting grooves 35 so that the assembling of the rotarydamper D is completed.

Next, operation will be explained.

First, as shown in a solid line arrow in FIG. 3, when the rotor 31rotates clockwise viewed from above, the resistive portion 36 rotatesclockwise inside the silicon oil 21, and viscosity resistance and shearresistance of the silicon oil 21 affect the resistive portion 36. As aresult, the rotation of the rotor 31 is damped.

Therefore, the rotation or movement of the gear wherein the driven gear71 being attached to the rotor 31 engages, rack and so on is damped andslowed down.

Herewith, when the rotor 31 rotates clockwise, a negative pressureportion is generated in lower ends of the depressed grooves 38 so thatthe air E being mixed into the case 11 during the assembling follows thenegative pressure portion and moves as shown in the solid line.

As shown in a dotted line arrow in FIG. 3, when the rotor 31 rotatescounterclockwise viewed from above, the resistive portion 36 rotatescounterclockwise inside the silicon oil 21, and the viscosity resistanceand shear resistance of the silicon oil 21 affect the resistive portion36. As a result, the rotation of the rotor 31 is damped.

Therefore, the rotation or movement of the gear wherein the driven gear71 being attached to the rotor 31 engages, the rack and so on is dampedand slowed down.

When the rotor 31 rotates counterclockwise as described above, the air Eshown in solid line in FIG. 3 heads toward the negative pressure portionbeing generated in the lower ends of the depressed grooves 38, so thatthe air E moves to a position shown in a doted line in FIG. 3 passingclockwise through the circumferential groove 13 a and the depressedgrooves 38, and moves following the negative pressure portion.

Herewith, the air E which moves from one arc-like through-bore 37 to theother arc-like through-bore 37 moves from one arc-like through-bore 37to the other arc-like through-bore 37, passing through thecircumferential groove 13 a and the depressed grooves 38 in a state ofbeing almost not compressed.

As described above, according to the first embodiment of the invention,in the resistive portion 36, the multiple arc-like through-bores 37 areprovided on a concentric circle, and the depressed grooves 38 connectingthe arc-like through-bores 37 are provided. As a result, during theassembly, the air E being mixed into the housing can be moved from onearc-like through-bore 37 to the other arc-like through-bore 37 in astate of not being excessively compressed.

Therefore, even if the rotor 31 rotates bi-directionally, the noisebeing caused by the air E being mixed into the housing can be prevented.

Moreover, since the circumferential groove 13 a is provided in the case11, during the assembly, the air E being mixed into the housing can bemoved from one arc-like through-bore 37 to the other arc-likethrough-bore 37 in a state of not being additionally compressed so thatthe noise being caused by the air E being mixed into the housing can beadditionally prevented.

FIG. 5 is a cross-sectional view of the rotor constituting the rotarydamper of the second embodiment of the invention; FIG. 6 is a plan viewof the rotor shown in FIG. 5; FIG. 7 is a bottom plan view of the rotorshown in FIG. 5; and the explanation is omitted by using the samesymbols for the same parts or corresponding parts of FIGS. 1-4.

Incidentally, the parts being omitted in the figures are constituted aswith the first embodiment.

In the figures, the plastic rotor 31 is constituted by: the axialportion 32 being housed inside the case 11 and whose one part projectsto the outside from the case 11; and a tabular resistive portion 36Awith a circle shape in plan view which is provided in the axial portion32 and moves through the silicon oil 21 inside the case 11.

The resistive portion 36A is constituted by: a thin-walled circular discportion 39, for example, whose 90-degree divided four circular notches40 are provided on the outer circumferential edge as the air retentionportions; and circular arc projections 41 being provided on the outercircumferential edge of the thin-walled circular disc portion 39.

Incidentally, as shown in FIGS. 5-7, the circular arc projections 41 areprovided above and below (both sides) of the thin-walled circular discportion 39.

An inner circular depressed portion 42 which is surrounded with thecircular arc projections 41 forms the air movement passage connectingthe notches 40.

Also, intervals of the circumferential direction of the circular arcprojections 41 are narrower than the greatest width (diameter) of thecircumferential direction of the notches 40. Right-and-left ends of thecircumferential direction of the notches 40 have the positionalrelationship of overlapping with the circular arc projections 41 in thecircumferential direction.

Next, since the assembly of the rotary damper D is the same as the firstembodiment, the explanation is omitted and the operation will beexplained.

First, as shown in a solid line arrow in FIG. 6, when the rotor 31rotates clockwise viewed from above, the resistive portion 36A rotatesclockwise inside the silicon oil 21, and the viscosity resistance andshear resistance of the silicon oil 21 affect the resistive portion 36A.As a result, the rotation of the rotor 31 is damped.

Therefore, the rotation or movement of the gear wherein the driven gear71 being attached to the rotor 31 engages, the rack and so on is dampedand slowed down.

When the rotor 31 rotates clockwise as described above, the negativepressure portion is generated in upper ends of the notches 40 so thatthe air E being mixed into the case 11 during the assembling follows thenegative pressure portion and moves as shown in solid line.

As shown in a dotted line arrow in FIG. 6, when the rotor 31 rotatescounterclockwise viewed from above, the resistive portion 36A rotatesclockwise inside the silicon oil 21, and the viscosity resistance andshear resistance of the silicon oil 21 affect the resistive portion 36A.As a result, the rotation of the rotor 31 is damped.

Therefore, the rotation or movement of the gear wherein the driven gear71 being attached to the rotor 31 engages, the rack and so on is dampedand slowed down.

When the rotor 31 rotates counterclockwise as described above, the air Eshown in solid line in FIG. 6 heads toward the negative pressure portionbeing generated in the upper ends of the notches 40, so that the air Emoves to a position shown with a doted line in FIG. 6 passing clockwisethrough the circular depressed portion 42, and moves following thenegative pressure portion.

Herewith, the air E which moves from one notch 40 to the other notch 40passes through the circular depressed portion 42 in a state of beingalmost not compressed, and moves from one notch 40 to the other notch40.

Even if the air E heading toward the other notch 40 out of one notch 40is centrifuged, the circular arc projections 41 lead the air E so thatthe air E is reliably moved to the other notch 40 from one notch 40through the circular depressed portion 42.

As described above, the second embodiment of the invention can achievethe same effect as the first embodiment.

FIG. 8 is an exploded perspective view of the rotary damper of the thirdembodiment of the invention, and the explanation is omitted by using thesame symbols for the same parts or corresponding parts of FIGS. 1-7.

In FIG. 8, the plastic rotor 31 is constituted by: the axial portion 32being housed in the case 11 and whose one part projects from the case 11to the outside; and a tabular resistive portion 36B with the circleshape in plan view which is provided in the axial portion 32 and movesthrough the silicon oil 21 inside the case 11.

The multiple arc-like through-bores 37 are provided on a concentriccircle centering on the center of the axial portion 32 in the resistiveportion 36B as the air retention portion.

Also, a circumferential groove 54 is provided on the lower side face ofthe cap 51, corresponding to the arc-like through-bores 37, on aconcentric circle centering on the center of the through-bore 52 as theair movement passage.

Incidentally, since the assembly and operation of the rotary damper Dare the same as those of the first embodiment, explanation thereof isomitted; however, the air E which moves from one arc-like through-bore37 to the other arc-like through-bore 37 moves from one arc-likethrough-bore 37 to the other arc-like through-bore 37, passing throughthe circumferential grooves 13 a, 54 in a state of being almost notcompressed.

Therefore, according to the third embodiment, the same effect with thefirst embodiment can be achieved.

Since the circumferential groove 13 a is provided in the case 11 and thecircumferential groove 54 is provided in the cap 51, the air E beingmixed into the housing during the assembly can be moved from onearc-like through-bore 37 to the other arc-like through-bore 37 in astate of being almost not compressed additionally. As a result, thenoise being caused by the air E being mixed into the housing can beadditionally prevented.

FIG. 9 is a cross-sectional view of the rotary damper of the fourthembodiment of the invention; FIG. 10 is a perspective view of the rotorshown in FIG. 9; and the explanation is omitted by using the samesymbols for the same parts or corresponding parts of FIGS. 1-8.

In these figures, the plastic rotor 31 is constituted by: the axialportion 32 being housed inside the case 11 and whose one part projectsto the outside from the case 11; and a resistive portion 36C which isprovided in the axial portion 32 and moves through the silicon oil 21inside the case 11.

The resistive portion 36C has a circle in plan view and is constitutedby: a tabular resistive-portion main body 43 which has a slightlysmaller diameter than the inner diameter of the cylindrical wall portion14 constituting the case 11; and thin-walled tabular air movementpassage formative projections 44 being provided on the outercircumferential surface of the resistive-portion main body 43, forexample, in a radial shape in order to form air movement passages 46 atintervals of 180 degrees.

Incidentally, an air retention portion 45 is formed outside (outercircumference) of the resistive-portion main body 43 being sandwiched inthe air movement passage formative projections 44, and the air movementpassages 46 become parts of above-and-below (both sides) of the airmovement passage formative projections 44.

Next, since the assembly of the rotary damper D is the same as that ofthe first embodiment, the explanation is omitted and the operation willbe explained.

First, as shown in a solid line arrow in FIG. 10, when the rotor 31rotates clockwise, the resistive portion 36C rotates clockwise insidethe silicon oil 21, and the viscosity resistance and shear resistance ofthe silicon oil 21 affect the resistive-portion main body 43. As aresult, the rotation of the rotor 31 is damped.

Therefore, the rotation or movement of the gear wherein the driven gear71 being attached to the rotor 31 engages, the rack and so on is dampedand slowed down.

When the rotor 31 rotates clockwise as described above, the negativepressure portion is generated in the lower ends of the air movementpassage formative projections 44, so that the air E being mixed into thehousing during the assembling moves following the negative pressureportion.

As shown in a dotted line arrow in FIG. 10, when the rotor 31 rotatescounterclockwise, the resistive portion 36C rotates counterclockwiseinside the silicon oil 21, and the viscosity resistance and shearresistance of the silicon oil 21 affect the resistive-portion main body43. As a result, the rotation of the rotor 31 is damped.

Therefore, the rotation or movement of the gear wherein the driven gear71 being attached to the rotor 31 engages, the rack and so on is dampedand slowed down.

When the rotor 31 rotates counterclockwise as described above, the air Ewhich was moving following the negative pressure portion being generatedin the lower ends of the air movement passage formative projections 44when the rotor 31 is rotating clockwise, heads toward the lower endswherein the negative pressure portion is generated and which become theopposite side of a circumferential direction of the air movement passageformative projections 44. As a result, the air E moves passing above andbelow the air movement passages 46 and moves following the negativepressure portion.

Herewith, the air E which moves from one air retention portion 45 to theother air retention portion 45 moves from one air retention portion 45to the other air retention portion 45, passing above and below the airmovement passages 46 in a state of being almost not compressed.

As described above, the fourth embodiment of the invention can achievethe same effect as the first embodiment. At the same time, since themultiple air retention portions 45 are formed between the outercircumferential surface of the resistive portion 36C and the innercircumferential surface of the case 11 in a circumferential direction,the air E being mixed into the housing during the assembly can bereliably located in the air retention portions 45.

FIG. 11 is an exploded perspective view of the rotary damper of thefifth embodiment of the invention; FIG. 12 is an expanded sectional viewof the left half of the case shown in FIG. 11; FIG. 13 is a plan view ofthe rotor shown in FIG. 11; FIG. 14 is a front view of the rotor shownin FIG. 11; FIG. 15 is a bottom plan view of the rotor shown in FIG. 11;FIG. 16 is a cross-sectional view taken along line XVI-XVI in FIG. 13;FIG. 17 is an expanded sectional view of the left half of a cap shown inFIG. 11; FIGS. 18, 19 are explanatory drawings of an assembling processof the rotary damper; FIG. 20 is a cross-sectional view of the rotarydamper of the fifth embodiment of the invention; and the explanation isomitted by using the same symbols for the same parts or correspondingparts of FIGS. 1-10.

In these figures, the plastic case 11 is constituted of: a case mainbody 12 wherein the cylindrical wall portion 14 circling the outer edgeof the bottom portion 13 whose planar shape is a circle is provided; thecylindrical axial supporting portion 16 being provided at the center ofthe bottom face of the bottom portion 13; and the mounting flanges 17with the mounting bores 18 being provided on the outer circumference ofthe case main body 12 at intervals of 180 degrees in a radial direction.

On the bottom face of the bottom portion 13, the circumferential groove13 a corresponding to the arc-like through-bores 37 of the rotor 31 isprovided as the air movement passage on the concentric circle centeringon the center of the axial supporting portion 16.

Also, on the upper side of the cylindrical wall portion 14, the circlingthin-walled projecting cylinder portion 14 a whose inner circumferentialface is the extended face of the inner circumferential face of thecylindrical wall portion 14 is provided. A circling diameter-openinginclination 14 b which expands toward a case main body 13 side isprovided on the boundary between the thin-walled projecting cylinderportion 14 a and the cylindrical wall portion 14 in order to weld theouter circumferential part of the cap 51.

Next, the plastic rotor 31 is constituted of: a cylindrical axialportion 32A; and a tabular resistive portion 36D which is continuouslyprovided in the axial portion 32A and has a circular shape in plan view.

The cylindrical cavity 33 wherein the axial supporting portion 16 of thecase 11 engages to be able to rotate is provided on the bottom surfaceof the axial portion 32A, and a step portion 34A is provided on the partprojecting from the cap 51.

Incidentally, the upper part of the axial portion 32A above the stepportion 34A has a square frustum 32 b which is concentric with the axialportion 32A and continuously provided on the upper side of a square pole32 a which is concentric with the axial portion 32A.

Also, in the plastic driven gear 71, a mounting bore 72A wherein adiameter-expansion step portion 72 b which is concentric with a squarehole 72 a is continuously provided is provided at the center on theupper side of the square hole 72 a.

Incidentally, in the embodiment, as shown in FIG. 12, the width of thecircumferential grooves 13 a, 54 a is wider than the width of thearc-like through-bores 37, and also the arc-like through-bores 37 arelocated inside the circumferential grooves 13 a, 54 a.

Next, an example of the assembling of the rotary damper D will beexplained.

First, as shown in FIG. 18, the axial portion 32A of the rotor 31 isfitted into the O-ring 61, and an appropriate amount of the silicon oil21 is injected into the housed portion 15. As shown in FIG. 19, a partof the axial portion 32A and the resistive portion 36D are housed insidethe housed portion 15 in such a way that the axial supporting portion 16of the case 11 is fitted into the cavity 33.

Incidentally, after the silicon oil 21 is applied to the cavity 33 andthe lower side (lower surface) part of the resistive portion 36D, theappropriate amount of the silicon oil 21 may be injected into the housedportion 15, and a part of the axial portion 32A and the resistiveportion 36D may be housed inside the housed portion 15 in such a waythat the axial supporting portion 16 of the case 11 is fitted into thecavity 33.

In this case, since the air stops retaining in the cavity 33 of therotor 31, the air remaining in the housing can be reduced.

Herewith, when one part of the axial portion 32A and the resistiveportion 36D are housed inside the housed portion 15, the silicon oil 21which is pushed by the resistive portion 36D and surfaced from thearc-like through-bores 37 gets through the O-ring 61, resistive portion36D, and axial portion 32A due to a capillary phenomenon because adistance a between the inner circumference of the arc-like through-bores37 and the O-ring 61 is closer than a distance b between the outercircumference of the arc-like through-bores 37 and the thin-walledprojecting cylinder portion 14 a. As a result, the O-ring 61 isprevented from sticking to the resistive portion 36D and the axialportion 32A, and the silicon oil 21 stops overflowing out of thethin-walled projecting cylinder portion 14 a.

The thin-walled projecting cylinder portion 14 a is fitted into thefitting depressed groove 55 of the cap 51 while the axial portion 32A isinserted into the through-bore 52, and the opening of the case 11 isblocked by the cap 51.

Herewith, when the opening of the case 11 is blocked by the cap 51, thesilicon oil 21 which is located near the O-ring 61 is compressed on theinner wall surface of the cap 51, and gradually moves toward the outsideof a circumferential direction. As a result, the air inside the housedportion 15 is pushed out from between the cap 51 and the opening of thecase 11 by the silicon oil 21, and in a state wherein the air remaininginside the housing becomes less, the cylindrical part of the outercircumferential edge forming the fitting depressed groove 55 of the cap51 abuts against the diameter-opening inclination 14 b, and the upperend of the thin-walled projecting cylinder portion 14 a and the bottomof the fitting depressed groove 55 are opposed with a small interval.

In this state, the cap 51 is pushed toward the case main body 12 with apredetermined pressing force, and the cylindrical part of the outercircumferential edge forming the fitting depressed groove 55 and thediameter-opening inclination 14 b are sealed, for example, while beingwelded in such a way of circling by high-frequency welding, and thebottom of the fitting depressed groove 55 is abutted against the upperend of the thin-walled projecting cylinder portion 14 a.

Herewith, when the cap 51 is welded into the case 11, the air E insidethe thin-walled projecting cylinder portion 14 a is mostly dischargedout of the case 11, and thin-walled projecting cylinder portion 14 a andthe cap 51 are attached firmly. At the same time, the O-ring 61 ishoused inside the diameter-expansion step portion 53, and the O-ring 61prevents the silicon oil 21 from leaking between the axial portion 32Aand the cap 51.

After the axial portion 32A projecting from the cap 51 is fitted intothe mounting bore 72A of the driven gear 71, the upper side part of thesquare frustum 32 b is heated, transformed, and expanded into thediameter-expansion step portion 72 b. As a result, as shown in FIG. 20,the assembling of the rotary damper D is completed.

As described above, the fifth embodiment of the invention can achievethe same effect as the first embodiment and the third embodiment.

Since the distance a between the inner circumference of the arc-likethrough-bores 37 and the O-ring 61 is made closer than the distance bbetween the outer circumference of the arc-like through-bores 37 and thethin-walled projecting cylinder portion 14 a, the silicon oil 21 getsthrough the O-ring 61, resistive portion 36D, and axial portion 32A dueto the capillary phenomenon during the assembling. Accordingly, theO-ring 61 is prevented from sticking to the resistive portion 36D andthe axial portion 32A, so that the silicon oil 21 stops overflowing outof the thin-walled projecting cylinder portion 14 a.

Therefore, the silicon oil 21 gets through the O-ring 61, resistiveportion 36D, and axial portion 32A, and the O-ring 61 can be preventedfrom sticking to the resistive portion 36D and the axial portion 32A. Asa result, an increase of early torque of the rotary damper D can beprevented. Also, the silicon oil 21 stops overflowing out of thethin-walled projecting cylinder portion 14 a so that the cap 51 can bereliably welded into the case 11, and the outer circumference of thehousing can be sealed.

Also, when the cap 51 is welded into the case 11, the upper end of thethin-walled projecting cylinder portion 14 a functions as a stopper sothat a height from the bottom portion 13 to the cap 51 can be setevenly. As a result, the distance from the resistive portion 36D to thebottom portion 13 and cap 51 can be held constant, and variation oftorque can be controlled.

In the first and fifth embodiments, an example with the circumferentialgroove 13 a is shown; however, even if the circumferential groove 13 ais not provided, the same function and effect can be achieved.

In case the circumferential groove 13 a is not provided, the airretention portions (arc-like through-bores 37) and the air movementpassage (depressed grooves 38) function in a similar fashion withoutbeing provided on a concentric circle.

Next, in the second embodiment, at least one of the circumferentialgroove 13 a and the circumferential groove 54 may be provided as shownin the third and fifth embodiments.

Also, in the third and fifth embodiments, an example with thecircumferential groove 13 a and the circumferential groove 54 is shown;however, if at least one of the circumferential groove 13 a and thecircumferential groove 54 is provided, the same function and effect canbe achieved.

Incidentally, the example that: the housing is constituted by the case11 and cap 51; the housed portion 15 of the silicon oil 21 is providedin the case 11; the through-bore 52 wherein the axial portion 32 of therotor 31 penetrates is provided in the cap 51; and the O-ring 61prevents the silicon oil 21 from leaking between the cap 51 and theaxial portion 32, is shown. However, the structure may be as follows.The housing portion of the silicon oil is provided in the cap, and thethrough-bore wherein the axial portion of the rotor penetrates isprovided in the case, so that the O-ring prevents the silicon oil fromleaking between the case and axial portion.

Moreover, the example that: the axial supporting portion 16 is providedin the case 11; and the cavity 33 is provided in the axial portions 32,32A, so that the rotor 31 is supported to be rotatable, is shown.However, the cavity may be provided in the case, and the axialsupporting portion may be provided in the axial portion.

Also, the example that the resistive portions 36, 36A-36D are integrallymolded in the axial portions 32, 32A is shown. However, the axialportions and resistive portions may be separately molded, and, forexample, rotate integrally in relation to a square shank and squarehole.

The example with the silicon oil 21 for the viscous fluid is shown;however, other viscous fluid which functions in a similar fashion, forexample, grease and so on may be used.

1. A rotary damper comprising: a housing (11); a viscous fluid (12)being housed inside the housing; a rotor (31) wherein a resistiveportion (36) which moves through said viscous fluid inside said housingis provided in an axial portion (32) being housed inside said housingand whose one part projects from said housing; and a sealing member (61)preventing said viscous fluid from leaking between said axial portionand said housing, and multiple air retention portions (37) are providedin said resistive portion (36) in a circumferential direction, and anair movement passage (38) connecting the air retention portions isprovided.
 2. A rotary damper according to claim 1, wherein said airretention portion is formed by a through-bore, and said air movementpassage is formed by a depressed groove.
 3. A rotary damper according toclaim 1, wherein said multiple air retention portions are formed in aconcentric circle, and said air movement passage includes acircumferential groove corresponding to said air retention portion andbeing provided in said housing.
 4. A rotary damper according to claim 1,wherein said multiple air retention portions are formed between theouter circumferential surface of said resistive portion and the innercircumferential surface of said housing in a circumferential direction.